Interaction of surfactants with model and biological membranes.: II. Effect of N-alkyl-N,N,N-trimethylammonium ions on phosphatidylcholine bilayers as studied by spin probe ESR
✍ Scribed by J. Gallová; F. Devínsky; P. Balgavý
- Publisher
- Elsevier Science
- Year
- 1990
- Tongue
- English
- Weight
- 794 KB
- Volume
- 53
- Category
- Article
- ISSN
- 0009-3084
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✦ Synopsis
The interaction of N-alkyl-N,N,N-trimethylammonium (C,TMA, n =6-18) salts (iodides and/or bromides) with model membranes prepared by hydration of egg yolk phosphatidylcholine (EYPC) over aqueous salt solutions has been studied by m-doxyl stearic acid (m-DSA, m = 12 and 16) spin probe method. In disoriented EYPC bilayers the C, TMA salts decrease the orientational order parameter $33 of m-DSA evaluated from the powder pattern ESR spectra. This effect is maximal for C6TMA. In oriented EYPC bilayers prepared by the parallel-beam sputtering method and hydrated over saturated NaCl solution the order parameter $33 calculated from the angular dependence of the nitrogen hyperfine splitting is decreased in the presence of C6TMA. The order parameter $11 obtained from the angular dependence of line positions indicates deviation of m-DSA motion from axial symmetry. CoTMA increases the probability of gauche conformations of the lipid chains by about 13-14%, and decreases the effective energy difference between the trans and gauche conformations by about 420--480J/mol, at molar ratio of EYPC/ C6TMA = 2:1. The angular dependence of linewidths is analysed by employing a theory of spin relaxation based on the strong collision model for molecular reorientations. The correlation time 70 of the reorientation of an axis orthogonal to the doxyl ring of 16-DSA is decreased in the presence of C6TMA, while that of 12-DSA is not influenced by it. The ratio of ~2/% is increased in the presence of C6TMA for the both spin probes. The results are explained using the free-volume model of the CnTMA-EYPC membrane interaction.